This invention relates to a novel peptide and more particularly to a unique octapeptide which is useful as an inhibitor of myristoylating enzymes.
Fatty acid acylation of specific eukaryotic proteins is a well established process which can conveniently be divided into two categories. On the one hand, palmitate (C.sub.16) is linked to membrane proteins via ester or thioester linkage post-translationally, probably in the Golgi apparatus.
On the other hand, it is known that myristate (C.sub.14) becomes covalently bound to soluble and membrane proteins via amide linkage early in the protein biosynthetic pathway. In the N-myristoylated proteins, amino-terminal glycine residues are known to be the site of acylation. See Aitkin et al., FEBS Lett. 150, 314-318 (1982); Schultz et al., Science 227, 427-429 (1985); Carr et al., Proc. Natl. Acad. Sci. USA 79, 6128-6131 (1982); Ozols et al., J. Biol. Chem. 259, 13349-13354 (1984); and Henderson et al., Proc. Natl. Acad. Sci. USA 80, 339-343 (1983).
The function of protein N-myristoylation is only beginning to be understood. Four of the known N-myristoyl proteins --p60.sup.src, cyclic AMP-dependent protein kinase catalytic subunit, the calcineurin B-subunit, and the Murine Leukemia Virus oncogenic gag-abl fusion protein-- are either protein kinases or a regulator of a phosphoprotein phosphatase (calcineurin) which modulate cellular metabolic processes. For p60.sup.v-src, it has been shown that myristoylation is required for membrane association and expression of this protein's cell transforming potential. See Cross et al., Molec. Cell. Biol. 4, 1834-1842 (1984); Kamps et al., Proc. Natl. Acad. Sci. USA 82, 4625-4628 (1985).
The development of relatively short synthetic peptides which can be conveniently made by synthetic peptide synthesis would be highly desirable for identifying and in studying the regulation of enzyme action in fatty acid acylation. Such peptides could serve as synthetic substrates for the myristoylating enzyme in yeasts and mammalian cells. They could also serve as highly specific competitive inhibitors of the naturally-occurring substrates. Novel synthetic peptides which thus serve as substrates of myristoylating enzymes are disclosed in copending U.S. patent application Ser. No. 924,543, filed Nov. 29, 1986, which is a continuation-in-part of U.S. patent application Ser. No. 894,235, filed Aug. 7, 1986. A preferred example of such substrates is the octapeptide EQU Gly-Asn-Ala-Ala-Ala-Ala-Arg-Arg.
Novel synthetic peptides which serve as inhibitors of myristoylating enzymes are disclosed in co-pending U.S. patent application Ser. No. 894,185, filed Aug. 7, 1986. Preferred examples of such inhibitors are the octapeptides EQU Gly-R-Ala-Ala-Ala-Ala-Arg-Arg,
wherein R=Tyr or Phe.
Corresponding octapeptides wherein R=Leu or Val likewise are inhibitors but they also serve as substrates of myristoylating enzymes.
The myristoylation reaction can be represented as follows: ##STR2##